Portable battery operated radio communication units are used extensively in the radio communication industry. Common battery operated units include pagers and cellular phones. A feature generally considered an important aspect to consumers in selecting these products is the battery life performance of the portable radio unit.
Presently, portable radio units use conventional circuits and software techniques to determine when the battery of a portable unit has expired. Generally, when an Alkaline battery discharges, its internal resistance (Rs) rises. This resistance has an adverse effect on the battery life performance of a portable unit. This is especially apparent in portable units, such as pagers, which use low voltage batteries such as, for example, a 1.5 V AA cell. To increase battery life, the radio receiver of a portable unit is not operated continuously, but is instead strobed on and off. While operation in this manner extends battery life, each time the receiver is turned on, a large current pulse, or "inrush current," is drawn from the battery to, for example, charge filter capacitors that have discharged during the time the receiver is off.
Typically, to power the receiver a 1V regulator is used. Under ideal conditions, the receiver should be able to operate until the battery nearly reaches 1V. However, because of a buildup in the internal resistance of the battery, the inrush current experienced when the receiver is initially turned on, can cause the battery terminal voltage to drop below the minimum operating voltage of the radio receiver, thereby preventing the pager from operating properly and degrading battery life.
To avoid such a failure, present battery management techniques used in low power consumer products activate, for example, a visual signal on a display of the portable unit warning a user that the battery has expired and must be replaced. Generally, this warning signal is asserted when the battery terminal voltage has reached a predetermined voltage (e.g., 1.1 V.+-.50 mV). This warning signal may be triggered even though under a lightly loaded situation (i.e., no inrush current from enabling the receiver) the battery terminal voltage is substantially higher, e.g., 1.2 V. Consequently, present battery management techniques result in a premature replacement of batteries.
Accordingly, what is needed is a battery management scheme that overcomes the foregoing disadvantages described in the prior art.